In case where an exhaust gas purification device constructed to include a catalyst is arranged in an exhaust passage, a precatalyst having an oxidation function may be arranged in an exhaust passage at a location upstream of the exhaust gas purification device. In this case, as such an exhaust gas purification device, there can be exemplified a NOx storage reduction catalyst (hereinafter referred to as a NOx catalyst), a particulate filter (hereinafter referred to as a filter) with a catalyst carried thereon, one having these NOx catalyst and filter in combination, and so on.
In addition, a reducing agent addition valve for adding a reducing agent to an exhaust gas may be further arranged in the exhaust passage at a location upstream of the precatalyst. In this case, when the exhaust gas purification device is raised in temperature or the air fuel ratio of an ambient atmosphere of the exhaust gas purification device is decreased, so as to recover the function of the exhaust gas purification device, the reducing agent is added to the exhaust gas by the reducing agent addition valve, whereby the reducing agent is supplied to the precatalyst and the exhaust gas purification device.
Japanese patent application laid-open No. 2005-127257 describes a technique in which a reforming catalyst for reforming the fuel supplied is arranged in an exhaust passage at an upstream side of a NOx catalyst. Further, Japanese patent application laid-open No. 2005-127257 describes a technique in which a reforming catalyst is disposed in a central portion of an exhaust passage, and a bypass circuit through which an exhaust gas flows is formed on an outer periphery of the reforming catalyst.